1. Field of the Invention
The present invention relates to a switching power supply control device and a switching power supply which perform a phase-lead compensation.
2. Related Background Art
Switching power supplies, which have such characteristic features as small size, light weight, and high efficiency, have widely been utilized as power sources for microcomputers built in various devices, personal computers, and the like. The personal computers and the like have been achieving a lower voltage and a higher processing speed while increasing their current consumption. Therefore, the switching power supplies may drastically increase or decrease their load current in response to the processing load in the personal computers and the like. The switching power supplies also have a characteristic feature in that they can easily conform to a wide input voltage range, and thus have been utilized as a power source usable in several countries in the world and a power source having a wide specification for setting their input voltage. It is necessary for the switching power supplies to secure a stable output voltage against such a change in load current and input voltage. Even when the output voltage becomes a transient response to a drastic change in load current or in input voltage, the switching power supplies are required to restore a stable state rapidly.
In particular, a high-speed response is required in switching power supplies for driving microprocessors such as VRM (Voltage Regulator Module) and POL (Point of Load) and LSI (Large Scale Integration) having a high clock frequency and a low voltage such as DSP (Digital Signal Processor) in order to respond to drastic fluctuations in load current. However, in a switching power supply equipped with an LC filter circuit as an output circuit, a phase delay occurs therein due to the influence of the LC filter circuit.
A switching power supply may have a control device such as a controller IC (Integrated Circuit), which turns on/off a switching device such as FET (Field Effect Transistor). The control device feeds back the output voltage of the switching power supply, so as to construct a voltage loop, and generates a PWM (Pulse Width Modulation) signal for turning on/off the switching device according to the output voltage. “An Accurate and Practical Small-Signal Model for Current-Mode Control,” Ridley Engineering inc., 1999 discloses the control device that feeds back the current flowing through an inductor of the LC filter circuit, so as to construct a current loop, thus performing a phase-lead compensation under current mode control using the current flowing through the inductor. In the current loop, a value resulting from multiplication of a detected current by a current control gain is fed back. The above document discloses that the current control gain has the optimal value. Data Sheet of HIP6301 PWM controller, intersil corporation, 2002, discloses that the current flowing through the inductor is detected according to a voltage across the resistance, Ron, of the switching device when the switching device is turned on.